Crews were first called to a home near NE 23rd and I-35, checking on smoke at about 7 a.m. Firefighters say they believe it started in the a back bedroom.

Firefighters say there was no one inside the vacant home.

Crews ran into obstacles extinguishing the flames.

"We had some difficulties with a floor furnace," said District Chief Lance Burnett with the Oklahoma City Fire Department. "One of the firefighters kind of got his foot hung up in the floor furnace, and once that happened, at the same time, the fire continued to progress."

It was too dangerous to fight from the inside. Outside, firefighters had to contend with an icy driveway, freezing hoses, and ice forming on the outside of gear.

Later in the afternoon, there was another fire near NE 23rd and Sooner at a vacant building firefighters said used to be a Catholic school.

Even though the building is vacant, they've been called out to it several times in the past.

Firefighters are still investigating but it's believed to have been started by people trying to stay warm.

"Vacant structures do make it a little bit more difficult," said Maj. Peter Sutterfield with the Oklahoma City Fire Department. "Believe we had possible transients that have come in and trying to warm themselves in this cold, cold weather and caught some trash on fire."

Firefighters are reminding people that they're checking and installing smoke alarms.